The type of seal with which the present invention is concerned is designed for use with pumps in a harsh environment of slurry and/or precipitative liquids. The seal assembly serves to separate and seal a rotary drive shaft to a centrifugal pump housing having a shaft opening through which the shaft extends. The seal assembly, generally includes a nonrotating seal ring connected to the pump housing and a rotatable seal connected to the pump shaft, each seal ring having a lapped seal face opposing the seal face on the other ring. One or both of the seal rings may be axially movable and resiliently urged toward one another by springs or other independent devices to assure seal face engagement.
Inherent problems result when seals are disposed in harsh environments involving slurries and/or precipitative fluids. In such environments, the normal radial deflections and errors of positioning the pump shaft are greatly exaggerated. Moreover, problems caused by abrasion and corrosion of the parts and jamming of the springs by solids and precipitates are ever present. Unless extraneous and costly devices are used in conjunction with the seal assembly, conventional seal designs are impractical in such environments. That is, unless a separate cleansing fluid flow is continuously provided for a conventional seal assembly, a brittle hard precipitate accumulates about and eventually encrusts the seal assembly thereby reducing the flexibility between the seal faces ultimately destroying the seal's effectiveness. As may be appreciated, there are substantial commercial and practical advantages in operating a pump with little or no such extraneous cleansing equipment and/or liquids.
In answer to Industry's problems, my above mentioned patented seal, because of its unique design, has proven very effective for use with centrifugal pumps moving abrasive slurry and/or precipitative fluids under pressure. My patented seal comprises the customary stationary and rotatable seal rings, each having a seal face in juxtaposed relation. The seal rings are resiliently urged into a sealing relationship by at least one elastomeric assembly. The elastomeric assembly includes an annular elastomer ring which is chemically bonded to a pair of radially spaced inside and outside metal bands or rings. The outside support ring and a portion of the elastomer body are exposed to the pump product while the inside ring is removed from the pressurized/corrosive pump product and serves to operatively connect the elastomer assembly to the pump housing. The design is such that the assembly supports one of said seal rings such that the elastomer body disposed between the support rings is placed in shear when the seal is assembled in place within the pump housing. This design allows the elastomer body to absorb the radial forces that are inherent with centrifugal pumps and permits limited radial shifting between the seal rings.
Despite these advantages, difficulties have been encountered when the seal assembly is disposed in an environment wherein a highly corrosive and/or caustic matter is being pumped under elevated pressures. Because the outside ring and the elastomer body are exposed to pump product, the chemical agent which bonds these elements into an operative assemblage is subject to attack by the pump product. In those applications where the caustic nature of the pump product has a greater corrosive effect on the bonding agent than it does on the elastomer itself, the pump product attacks and deteriorates the chemical bond joining the support ring to the elastomer body. Eventually, the bond fails thus resulting in premature seal failure.